The present invention relates to a method and plant for treatment of wood blanks and rotary cut veneer.
In the known plants, blanks and rotary cut veneer are passed through a dryer at whose outlet the sheets are stacked and sent in packs to the subsequent operations.
From normal dryers the product emerges severely undulated. There have therefore been proposed separate flattening treatments.
These treatments are performed before using the blanks and rotary cut veneer by placing the packs in purposeful presses. These presses are made up of two pressing tables in sequence, one heated and one cooled, usually served by a single conveyor belt which takes the packs from one table to the other.
Each pack is subjected to a first pressing under the hot table. The hot press flattens the material and the heat makes the wood malleable. The stay time under the hot press depends on the type of material and the thickness of the pack. Indeed, time is necessary waiting for the heart of the pack to reach the preset temperature also.
When the hot pressing operation is completed the press opens and the hot pack is conveyed under the cooled pressing table. The cold press closes on the pack, pressing it again but also removing heat from the wood by means of the refrigerating liquid running in the press table. Once the cold press is closed, it is again necessary to wait for the entire pack to cool to the preset temperature. This way the flat form of the sheets reached in the hot press stabilizes and the cold press can be opened and the pack is unloaded.
The pack treatment described above generates a considerable loss of time and can cause deformities among the outermost sheets and the more inward sheets in the various packs.
To remedy this there have been proposed dryers termed `stretching dryers` in which during drying the sheet are subjected to a simultaneous stretching operation in order to avoid the subsequent pressing operation with hot-cold cycle. Although the sheets come out of these dryers flatter there can still remain residual undulations not always tolerable. In addition the stretching dryers are more costly and cumbersome and suffer from greater operating costs.
The general purpose of the present invention is to remedy the above mentioned shortcomings by making available a method and a drying plant delivering sheets with optimal planarity, rapidly and with relatively reduced costs and space occupied.